Door constructions like this are generally used as pressure doors and gas tight doors of air raid shelters and similar spaces. The doors and their locking devices are usually solid and simple in structure, e.g. in order that they would endure considerable impact stresses and compression loads and that they could be opened and closed easily and quickly and that their tightness could be secured in the long term.
In known solutions, the locking device often consists of some kind of wedge arms or bars catching behind the frame or behind a ridge formed in the frame or possibly in a reaming made into the frame. As to the actual closing function, these locking devices operate relatively satisfactorily, especially in normal circumstances. In critical situations, as for instance in connection with bomb explosions, heavy firing and the like, the drawbacks of the known solutions appear clearly, however.
Strong pressure waves caused by explosions and exponential decreases of pressure thereafter, the influence of which is mainly directed rather vertically toward the surface level of the door construction in question, make the door construction shake and tremble strongly in the horizontal direction, because the known locking devices are not able to receive such loads. In these situations occur also loads substantially parallel with the surface level of the door construction and caused by quaking ground, which loads again make the door construction shake strongly also in the vertical direction. Efforts have been made to eliminate the drawbacks of these last-mentioned loads by installing supporting frames in the door panels of the door construction, the purpose of which supporting frames is to support the door panel with respect to the frame. Their effective influence is, however, relatively small because of the fact that the door panels do not remain in place in the frame on account of the first-mentioned loads. Consequently, the result is that the locking devices get broken and the door panels finally come loose from the frame. It is quite clear that the tightness of the doors suffers already during slighter shakings and tremblings, which cannot be allowed as far as gas tight doors are concerned.